It's odd to find characters in a science-fiction novel repeatedly announcing that they hate science fiction. I can only suppose that Jeanette Winterson is trying to keep her credits as a "literary" writer even as she openly commits genre. Surely she's noticed that everybody is writing science fiction now? Formerly deep-dyed realists are producing novels so full of the tropes and fixtures and plotlines of science fiction that only the snarling tricephalic dogs who guard the Canon of Literature can tell the difference. I certainly can't. Why bother? I am bothered, though, by the curious ingratitude of authors who exploit a common fund of imagery while pretending to have nothing to do with the fellow-authors who created it and left it open to all who want to use it. A little return generosity would hardly come amiss.

The Stone Gods opens rather unfortunately with such meaningless flourishes as the "yatto-gram" and some fancy writing - "Eggs, pale-blue-shelled, each the weight of a breaking universe." Most of that gets done with early on, and Winterson settles into telling her story, which is complex, interesting and doom-laden. Perhaps there is an excess at times of the device known to science-fiction writers as "As you know, captain. . ." These are the scenes where one character explains to another character all about something the other character obviously knows. Realistic fiction, dealing with the familiar, seldom needs such a device, but imaginative fiction often has to explain what a hobbit or a light year or a limbic pathway is. And so we get dialogue beginning: "Oh, Spike, you know the theory," followed by a lecture on the theory. But even in the lectures Winterson's tone is lively. Her wit varies from flashy to flashing, her highly mannered, crackling dialogue moves things right along, the surface of her tale scintillates. Underneath it, as in every fable telling us that the future will be much worse than we thought, things are deadly serious.

"What is it about?" "A repeating world." So the narrator Billie Crusoe tells us, talking about a book she's picked up in the Tube, called The Stone Gods.

So, yes, we are near Borges country. And beyond that, it's hard to discuss the story without entirely giving away the central conceit, which Winterson develops teasingly, gradually. Delayed revelation is an essential effect in the book, and I don't want to spoil it. But, since there are some apparently arbitrary initial confusions, I want to assure other readers that it does all add up. We will come to see the connections. We will understand why, from the interplanetary cataclysms of the first section, we are shifted so abruptly to the visit of Captain Cook's ship to Easter Island, and from that taken suddenly to a near-future London, and also why certain characters have the same names though they don't inhabit the same spacetime.

Some of these significantly hidden connections are made with truly charming inventiveness. In the first section, the reduction of the robot Spike to a mere head is grotesquely sad; in the last section, Spike's existence as a mere head that doesn't have its body yet is grotesquely funny, particularly when Spike succeeds, as I think no other detached head has, in having sex. And when Billie Crusoe finally finds her Man Friday, the ironic comedy is fine.

At times Winterson seems to think that poetical invention excuses fictional implausibility or incoherence. A farmhouse, with hearthfire, beside a willow-hung river complete with iris and moorhens could not possibly exist in the terminally exhausted world of the first section. But since this image of the farm is essential to the book, it is essential that we be able to believe in it.

Bursts of emotion may be forgivable, given the dire events recounted and predicted, but they may also be overwrought. I felt this particularly in the Easter Island section, the central part and hinge-point of the book. The history of that island and its people, as it has been pieced together in recent years, is in itself so appalling, and so appallingly apt an image of human misuse of our world, that it needs no heightening to make it hit home. But here it is all mixed up with a love story that is asked to carry far too much weight. Sentimentality, the product of a gap between the emotionality of the writing and the emotion actually roused in the reader, is very much a matter of the reader's sensibility; to me, both the love stories in the book are distressingly sentimental.

Still, despite the gaspy bits, the purple bits, and the lectures, The Stone Gods is a vivid, cautionary tale - or, more precisely, a keen lament for our irremediably incautious species.

· Ursula K Le Guin's Changing Planes is published by Gollancz. To order The Stone Gods for £15.99 with free UK p&p call Guardian book service on 0870 836 0875.